Narcissus alkaloids (pseudolycorine and residual alkaloid) possess remarkable prolongation effect on the life span of advanced Rauscher leukemic mice in comparison with standard drugs (cyclophosphamide, vincristine, 6-MP, methotrexate, 5-FU, dactinomycin, daunorubicin, BCNU and azacytidine); interferon inducers (poly I:C and tilorone); immunostimulator (levamisole) or reverse transcriptase inhibitors (rifamycin SV and ethidium Br.). The combined treatment with several cytotoxic drugs increases the effectiveness. The alkaloids are not inhibitory to humoral and cellular immunity and interferon induction systems by the long-term administration. The alkaloids inhibit the growth of Rauscher virus in cell cultures; the residual alkaloid inhibits reverse transcriptase and the active principle is now identified as pretazettine (C18H21NO5). The proposed project is the further basic studies of the alkaloids necessary before their possible clinical application, and include: 1) Large scale production of pretazettine and pseudolycorine for pharmaco-toxicological studies in bigger animals, for chemical synthesis of the more active derivatives, and for the continuous supply to other laboratories. 2) Studies of pretazettine and the derivatives as inhibitors of reverse transcriptase in tube. 3) Studies of therapeutic effect of the alkaloids on spontaneous leukemia in AKR mice as a model of human acute lymphocytic leukemia. 4) Studies of the alkaloids on macromolecular synthesis in Rauscher leukemic cells in vitro. 5) Eradication of the leukemogenic genomes in Rauscher virus-carrying 3T3 cells in vitro. 6) Inhibition of malignant transformation or activation of C-type virus of 3T3 cells induced by chemicals by treatment with the alkaloids. 7) Trials to obtain a mutant Rauscher virus resistant to pretazettine or pseudolycorine and the sensitivity tests of the reverse transcriptase to pretazettine.